Fossilised air in the Polar ice caps
Over the years, continental ice caps form when snow accumulates and is packed down and transformed into ice by subsequent snowfalls. This ice contains bubbles of air as well as all sorts of airborne particles and pollen. Once this air is imprisoned in the ice, it conserves its original composition, so study of the air bubbles and their particles can yield invaluable information about the Earth’s climate in the past.

Ice cores: veritable time-travel machines
Scientists frequently take core samples of the polar ice. The further the core goes down, the older the ice sample, so by analysing older and older ice the scientists travel back in time, gradually writing the history of the Earth’s climate. A lot of data has been gathered by studying the Greenland ice cap, while the “climate archives” in the Antarctic have also yielded invaluable information.

The Greenland ice cap
In the thickest part of the Greenland ice cap, glaciologists have extracted and studied core samples from as deep as 3,050 metres before they struck the underlying rock. The cores contain ice that fell as snow over the past 2,500 centuries! And of course evidence of various climate fluctuations: droughts, climatic catastrophes, periods of global warming, ice ages, etc.

Our pollution is sealed up in the ice too
The bubbles of air trapped in the polar ice show that the amount of methane and CO2 in the atmosphere has increased markedly over the past two centuries, i.e. since the beginning of the industrial era. The more recent ice in Greenland also contains much more pollution than ice from the Antarctic, because of the proximity of human activity in the Northern Hemisphere.